Phi (letter)
| Greek letters | |
| Α α Alpha | Β β Beta |
| Γ γ Gamma | Δ δ Delta |
| Ε ε Epsilon | Ϝ ϝ Digamma |
| Ζ ζ Zeta | Η η Eta |
| Θ θ Theta | Ι ι Iota |
| Κ κ Kappa | Λ λ Lambda |
| Μ μ Mu | Ν ν Nu |
| Ξ ξ Xi | Ο ο Omicron |
| Π π Pi | Ϻ ϻ San |
| Ϙ ϙ Qoppa | Ρ ρ Rho |
| Σ σ Sigma | Τ τ Tau |
| Υ υ Upsilon | Φ φ Phi |
| Χ χ Chi | Ψ ψ Psi |
| Ω ω Omega | Ϡ ϡ Sampi |
| Greek alphabet | |
Phi (Φ φ), pronounced fee, is the 21st letter of the Greek alphabet and has a numeric value of 500.
The lower-case letter φ is used as a symbol for:
- Euler's totient function in number theory.
- The argument of a complex number in mathematics.
- The golden ratio in mathematics, art, and architecture.
- The value of a plane angle in physics and mathematics.
- The work function in electronics.
- The phase of a wave in signal processing.
- The magnetic flux in physics.